Beefing it up

Livestock production for human consumption is growing dramatically as developing nations increasingly eat meat. But the production of such animals adds to greenhouse gas emissions and takes up biomass production that could otherwise enter the human food chain directly. have calculated the possible impacts of livestock production between 2000 and 2050 in a new report in the Proceedings of the National Academy of Sciences (published online). " As of 2000 the livestock sector is estimated to have contributed 14 per cent of anthropogenic greenhouse gas emissions, 63 per cent of reactive nitrogen mobilization and consumed 58 per cent of directly used human appropriated biomass globally. " Using simplified and conservative models, the authors write, they estimate that production of livestock in 2050 at levels projected by the UN Food and Agricultural Organization may increase direct livestock-related greenhouse gas emissions from meat, milk and egg production in the order of 39 per cent, biomass appropriation by 21 per cent and reactive nitrogen mobilization by 36 per cent above reported 2000 levels. On current trajectories, it is estimated that anthropogenic climate change may increase global mean temperatures by 3ºC by 2100. As a rise of 2ºC above preindustrial levels may result in " dangerous climate change " with serious negative impacts to ecosystems and human welfare, this issue has moved to the fore in government policies around the globe, they write. The Intergovernmental Panel on Climate Change estimates the direct contribution from agriculture at 10-12 per cent of greenhouse gas emissions, without counting for the effect of clearing land for agricultural production. With that included, one recent study suggests that livestock production comprises 17–32 per cent of anthropogenic emissions. The EU has studied the issue, and concludes that food production contributes 31 per cent to total emissions, a large part of which is livestock production. Although nitrogen is essential to all life forms and is also the most abundant element in the Earth's atmosphere it exists there in a stable form inaccessible to most organisms until fixed in a reactive form. The supply of reactive nitrogen plays a pivotal role in controlling the productivity, carbon storage, and species compositions of ecosystems. Since the industrial revolution, annual anthropogenic reactive nitrogen emissions have increased to the extent that human activities now contribute more fixed nitrogen to terrestrial ecosystems than do all the natural systems combined. Background levels have effectively doubled since 1970 and continue …